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Author Topic: new user, lennox 296uh help with ECM fan speed and 2 stage heating  (Read 902 times)

Offline hellojtm

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Hi All,

I found the forum and have been searching all of the helpful responses.  Unfortunately I don't see a specific solution to my issue, but at least I see some confirmation that others have had and resolved similar issues.   Much appreciation in advance for any guidance, so, here goes....

I live in San Francisco, I'm a home DIYer and have a lot of free time, but a hardware engineer by trade, so I'm happy to learn and dive as deep as needed to do things myself for my own home.   That said I'm currently stumped trying to find technical info on my furnace.  It's a Lennox EL296UHE, and in a nutshell I'd like to reduce the fan speed.  The amount of air being pushed out of the registers is simply excessive.  For our purposes we'd much rather have a quieter experience, even if it means that the house is slower to warm up.   Prior to installing this high-efficiency unit we had a gravity fed furnace from the 1950s which basically trickled heat.  We were fine with that experience, but wanted to redo the ducting and improve efficiency.  So, what I'm getting at is that I'm ok with the furnace not kicking into the second stage of heating if that's what is required to reduce the fan speed.  I get the impression from the manual that the speed is adjustable (see imgur link and manual link below) but I wasn't able to determine precisely how to manage it.

Here is a link to the manual I have been working from: http://www.hvacpartsshop.com/manuals/el296uhe.pdf

Here are some images which I created when I started a thread on reddit, which eventually died without a conclusion :

http://imgur.com/a/en8zr

Here is the original reddit thread if anyone wants a little more history:

https://www.reddit.com/r/HVAC/comments/4ic4g4/question_lennox_el296_blower_motor_adjustment/

SO, would anyone be able to point me in the right direction to either:

-  trim down the max fan speed, in small steps
-  force the furnace to only use single stage and low fan speed
-  some other, more elegant, solution

thanks in advance!

Jesse

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #1 on: July 02, 2016, 11:07:59 AM »
You can download the Lennox EL296XE Installation Manual - Here

On page 40 you will see the blower speeds.
Black = high speed
Brown = med high speed
Blue = med low seed
Yellow = med speed
Red = low speed

If you don't have an air conditioner you will only need to adjust the high and low heat fan speeds.  Unpark the unused red low speed wire and attach it to the low heat, and move the yellow med speed wire to high heat.  You can park any unused fan speed wires on PARK.  It's important you check the rating plate and verify both the low heat and high heat temperature rise are within the rated limits.  Measure the heat from the supply plenum and the temperature inside the return air duct, and subtract the two to find the temperature rise.

The furnace is shipped as a two stage furnace requiring a two stage thermostat.  I'm not sure if your furnace is controlled by a single or two stage thermostat.  If the thermostat has W1 and W2 wires connected to the furnace, then dip switch 1 should be in the factory position, OFF.  See page 42.

How many BTU's is the furnace?

What is the model of thermostat?  Are both W1 and W2 wired?

What color are the wires currently connected to low and high heat fan speed terminals?

What position is dip switch 1 in, On or Off?

Offline hellojtm

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #2 on: July 02, 2016, 03:20:23 PM »
Hi Admin,

Thanks so much for your response.  If you look at the image here:

edit: removed this image link because the image was too large for the screen.  Please check out SECOND image in this gallery:
http://imgur.com/a/en8zr

You can see what I was lamenting about in the reddit thread.  There are no posts on my terminals on the board for me to park/unpark and re-configure the wiring for the fan speed.  One user commented that because I had an ECM motor the speed taps would be unusable, and suggested I need to set the DIPs, however I wasn't able to find out what to set the DIPs to, or if that was even valid.   Here is the image of the DIPs:

edit: removed large image again, please observe FIRST image in gallery above.

There are two sets of DIPs and you can see they are ALL set to the OFF/0 position.  The manual only seems to explain the DIP settings for the lower row of DIPs picture.  And of those only one pair, 6&7, are assigned to the blower motor, but they specifically state they are for the continuous fan mode.   It's set to the lowest speed currently (default).

The furnace is the EL296UH090 which is 90,000 BTU.  The house is 1500sf (give or take) all on one level.

Both W1 and W2 are wired to an EcoBee3 thermostat.

I hope I answered all the questions and you could help me further!

thanks in advance,
Jesse

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #3 on: July 02, 2016, 05:49:15 PM »
The EL296XE has a constant torque fan motor, which qualifies as an ECM.  The EL296XV had a true variable speed ECM fan motor.  If you don't see a red, orange, yellow, blue or brown wire connected to the motor, it's likely you have the more costly XV model.

If you look at the rating plate inside the furnace, what is the full model number?

Is there an air conditioner installed with that furnace?  If so, what size or model is it?

I would say that furnace is oversized and perhaps the ductwork cannot handle the CFM from a 90,000 BTU model.

If it's a XV model, then I will show you how to adjust the fan speeds.  There is a way we can reduce the airflow.

Offline hellojtm

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #4 on: July 02, 2016, 06:06:00 PM »
Hi,

Apologies for continually providing the truncated model number, here is the full number:

EL296UH090XV48C

Here is the fan motor plug:

http://imgur.com/AkFNxSW

We do not have an a/c compressor installed with this unit.  In San Francisco it is just so rarely needed...  but maybe in the future we would like to, when we are feeling more luxurious  ;D

I can give intimate details about the ductwork and registers if/when needed.  But, I would not disagree with your assessment that the furnace is likely oversized for our house.  I did try to do the ducts based on the furnace demands, but the registers themselves may be relatively restrictive. 

Jesse

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #5 on: July 02, 2016, 11:20:39 PM »
You can download the EL296XV Installation Manual and Data Guide - Here

Look at pages 49 and 50 in the EL296XV Installation Manual for the dip switch settings.  Look at page 33 in the EL296XV Data Guide for the fan speed data.

The EL296UH090XV48C furnace has a 1st stage heating CFM of 1210 and a 2nd stage heating CFM of 1285.  Forcing the furnace into 1st stage heating won't reduce the airflow much, but it may improve your comfort during the heating season if in fact the furnace is oversized at 90,000 BTU's.  The 1st stage has an output of 55,000 BTU's and the 2nd stage has an output of 85,000 BTU's.  I don't know the R-value of your home but I suspect the 1st stage heating would satisfy your heat loss.  To force the furnace into 1st stage heating only, turn off the furnace power and remove the W2 wire from the Ecobee thermostat.  Then turn the power back on and enter the Ecobee thermostat settings and turn the furnace from 2 stage to 1 stage heating.  Now the thermostat will only power the W1 terminal and 1st stage heating until it's satisfied.

I'm not sure if the thermostat and furnace have the G wire or if you're able to use the fan control option.  I'm also assuming the furnace has a single side return air connection.  If you turn the thermostat fan from AUTO to ON the continuous fan will run in the furnace.  The continuous fan operates at 38% of the 2nd stage cooling speed.  You're 2nd stage cooling CFM is 1565 so the continuous fan runs at 595 CFM.  If you install an AC it will need to be sized for your home.  Assuming you install a 2 ton AC you could turn dip switches #5, #6, #8 and #15 to ON to set the 2nd stage cooling to 910 CFM which would reduce the continuous airflow to 255 CFM.  If you install an AC larger than 2 ton you must ensure the cooling speed is increased.  If you installed a 3 ton AC turn dip switches #5, #8 and #15 to ON to set the second stage cooling to 1275 CFM.  Make sure if you install a single stage AC you wire the Ecobee Y1 to the furnace Y2.

To adjust the heating speed turn dip switches #12 and #13 to ON, which will reduce the 1st stage heating speed by 18%, from 1210 CFM to 990 CFM.  Hopefully the air flow noise is more bearable.  You have to verify the temperature rise is still within the rated limit.  Your furnace 1st stage heating temperature rise is rated 30F - 60F.  If you measure the temperature inside the return air duct, subtract it from the temperature inside the supply plenum to get your temperature rise.  If the temperature inside the supply plenum is 130F and the temperature inside the return air duct is 72F, the temperature rise is 58F, and within the rated limit.  If the supply temperature is 140F the temperature rise if 68F and above the rated limit.  To lower the temperature rise you must increase the airflow.  Without AC your return air temperature could be higher than during the heating season, so will want to do this test then.

Offline hellojtm

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #6 on: July 03, 2016, 09:10:11 PM »
Admin,

I read this thoroughly as well as the noted pages in each manual.  Everything you wrote makes perfect sense and is quite inclusive!   It seems that with those two manuals and a few hours time I could have arrived at the same solution you suggested.

I'll reply back once I've completed this, just to close the thread out for anyone that may search in the future.  To respond to one of your assumptions, yes we have a single side air return.

 8..

Jesse

Offline hellojtm

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #7 on: July 03, 2016, 09:47:54 PM »
OK.  The DIP switch portion is complete.

- switched 12, 13 to ON
- didn't remove W2 yet
- didn't alter cooling fan speed or continuous mode fan speed

The real test will be tomorrow morning when the heater comes on about 4am.  If the register in the bedroom is still making a train whistle sound we'll take the next step and disable stage II heating!

Looking at other furnaces in the data sheet I'm disappointed we didn't go with a lower volume model.  I'm sure it would have been cheaper as well.  Live and learn!

Is it OK if I link this thread back to the reddit forum in case it helps someone in the future?

thanks again,
jesse

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #8 on: July 04, 2016, 05:29:26 AM »
Quote
Is it OK if I link this thread back to the reddit forum in case it helps someone in the future?

Yes, that's okay.

BTW, which vent is whistling, the supply air or return air vent?  You may need to add some return air openings to the duct design.

Offline hellojtm

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Re: new user, lennox 296uh help with ECM fan speed and 2 stage heating
« Reply #9 on: July 04, 2016, 10:39:38 AM »
Here is the noisy register in the bedroom.  It looks like a noisy vent style to me, as well.  So there is room for improvement there.

http://imgur.com/k3ms1H1

I went ahead and disabled the 2nd stage on the furnace.   It was marginally too loud when the 2nd stage kicked in this morning.   If all goes well tomorrow morning then I'll leave it like this, at least until the actual winter comes.